Electrical system for exploring drill holes



y 22, 1941. I E. e. LEONARDON ELECTRICAL SYSTEM FOR EXPLORING DRILL HOLES Filed Nov. 2a, 1938 2 Sheets-Sheet 1- EUGENE G. LEONARDON July 22, 1941. E. G. LEONARDON.

ELECTRICAL SYSTEM FOR EifiLORING DRILL HOLES Filed Nov. 28, 1958 2 Sheets-Sheet 2 //Z .4. W awe/whom EUGENE G.LEONARDON x N M /LM 94%W/ mew- Patented July 22, 1941 2,249,769 ELEc'rRIcKi. SYSTEM FOR EXPLORING DRILL HOLES Eugene G. Leonardon, Houston, Tex., assignor to Schlumbergcr Well Surveying Corporation, Houston, Tex., a corporation of Delaware Application November 28, 1938, Serial No. 242,864

11 Claims.

The present application is a continuation-inpart of application Serial No. 85,180, filed June 13, 1936, for Method and apparatus for exploring drill holes.

The herein described invention relates to means for investigating the geological strata traversed is ordinarily consumed by methods commonly employed heretofore.

For the attainment of the above stated object this invention provides means for continuously testing the formations at the bottom of the drill hole while the drilling proceeds, that is to say, without any interruption thereof.

The invention includes means whereby the resistivities of strata traversed by a drill hole may be measured or indicated during the drilling operation at successive levels as they are contacted by the drill bit, and before they have been flooded by the liquid (water and mud) of the drill-hole. It also includes means for measuring-without interrupting the drilling operatiorr-the differences of potential that spontaneously exist in the drill-hole.

The invention also includes a novel bit-structure whereof at least one insulated electrode forms a permanent part.

The accompanying drawings illustrate diagrammatically, and by way of non-limiting examples, means whereby the invention may be successively carried out in practice.

Fig. 1 is a view, in vertical section with respect to the drill hole, the drilling mechanism being shown in elevation with part of the drill bit in section;

Fig. 2 is a view in vertical section, showing the principal parts of the drilling mechanism;

Fig. 3 is a diagram in vertical section, illustrating an embodiment of the invention which is suitable for measuring the resistivities of the formations during the drilling operation;

Fig, 4 is a similar view of a modified form of the embodiment shown in Fig. 3.

Referring to Figs. 1 and 2, the drill hole I may be filled as usual with liquid 2, although in some cases no liquid is present. In said hole are the usual rotary drill pipes, to the lower part 3 of which the bit 4 is fastened. Bit 4 is provided with an electrode 5 which is insulated from the bit itself by means of insulating material 6, rubber or Bakelite for instance, and to it is connected an insulated wire I, which passes through the bit, its upper end being attached to a special connector 8, in the form of a socket (Fig. 2). The wire 1, connector 8 and the electrode 5 are inserted into the bit 4 in such locations and in such manner that they do not interfere with the circulation of fluid through said bit during the course of the drilling. It is commonly the practice to cause a circulation of the fluid during the drilling in order to carry out of the drill hole the debris which otherwise would accumulate at the bottom thereof and interfere with the drilling. To this end the drill-hole fluid is pumped under pressure into the drill pipe and emerges around the bit, whence it is forced upward through the annular space outside the drill pipe. It is of course desirable that the openings (not shown in the drawings) through which the fluid passes should not be obstructed. Therefore the electrodes and the conductors leading to them should be so disposed that they do not interfere with the circulation of said fluid during the drilling operation. This is readily accomplished by placing the several parts in recesses formed in the drill bit at suitable locations.

The drawings are not to be taken as indicating the size of the electrode relative to that of the bit, but merely as illustrating a suitable location for the electrode and its circuit connections. Its relative size is a matter of technical judgment and is readily determined. This applies also to the embodiments of the invention illustrated in Figs. 3 and 4.

Through the interior of each drill pipe section extends a single insulated wire cable. 9 i Fig. 2), which is somewhat longer than the drill pipe. The wire composing said cable should be mechanically of high quality. It might. for instance, be covered by a steel braid and it must be flexible enough to resist large and frequent twistings. The upper end of cable 9 is provided with a special insulated connector l0, affordin an easy and solid connection with the lower end ll of the wire l2 fixed in the section l3 next above of the drill pipe. This connection may be of the screw and threaded socket type, as indicated. Each wire is fixed permanently as at '4 inside and at the top of the drill pipe hole. The fastening means is so constructed that it does not impede the circulation of the mud inside of the pipe.

The grief stem I5 is also equipped in a similar manner. However, the upper end of the cable 9a,

face.

within stem I5, is connected with a horizontal insulated metallic member IS, the other end of which is soldered to an insulated slip ring I! which encircles the grief stem IS, the latter being grooved at this place to receive said ring.

A brush I! is held in contact with ring II by means of 7 an insulated arm l3, fixed to swivel 20 screwed at the upper part of grief stem 15. As is known, the u per part of the swivel 20 is not rotated during the drilling operation.

Wire 2| is soldered at one end to brush I 8, its other end being connected with one of the terminals of a potentiometer 22, or other suitable measuring instrument. The other terminal of the measuring instrument 22 is connected with a low resistance ground 23 (Fig. 1).

Obviously the construction described above may be modified in many details without departing from the spirit or the substance of the invention. For instance, the insulated wire inside the drill pip might be replaced by an insulated rod soldered to the inner part of said pipe with suitable contacts at each joint.

As is readily to be seen from the drawings, meter 22 measures the differences of potential which exist between electrode located at the bottom of the hole and electrode 23 at the sur- It is a well known fact that those differences of potential are characteristic of the nature of the formations traversed as well as of their fluid content.

The operation is as follows:

As the drilling proceeds in the usual manner, the measuring instrument 22 is under continuous observation and notation is made of the depth of the hole by observing the positions of the drill stem. All this information can be automatically recorded on a diagram by known methods and appliances as the drilling proceeds. Such diagrams show in abscissae the depth at which the measurement has been made and in ordinates the value of the potential or other characteristic of the formation at the point of observation.

When the bit passes into a porous formation the potential in the vicinity of the drill bit will immediately change with the accompaniment of a pronounced kick on the diagram, thus indicating the possible presence of water, oil or gas. If it is desired to check the information more closely the drilling can be stopped, the drilling mechanism removed, and the level examined by a drill stem test or by any other appropriate procedure.

It is obvious that the construction shown is capable of numerous modifications, which are to be considered within the spirit and intent of the invention and within the scope of the appended claims.

Inparticular it is evident that the electrode 5 can be inserted at any place in the bit or in the drill pipes where it can operate advantageously for obtaining the desired results. Furthermore, if it is technically desirable, the reference electrode 23 can b placed inside the drill hole. to be investigated, or in any other hole, or it can be inserted in the bit or in the drill pipe.

Figs. 3 and 4 show embodiments of the invention which are adapted to the particular purpose of obtaining measurements during the course of the drilling operation of an electrical characteristic (specially the resistivity) of strata traversed by the drill and before they have been flooded by the bore-hole liquid.

Except as hereinafter specified, the construction and operation of the several parts of the system illustrated in Figs. 3 and 4 are, or may be, such as described above in connection with Figs. 1 and 2.

In the particular measurements for which the embodiments of the invention shown in Figs. 3 and 4 are primarily intended, that is, for the measurement of an electrical characteristic particularly the resistivity) at the place of earth contact with the bit, at least one insulated electrode will be incorporated in, or carried by, the bit itself, said electrode being preferably of small dimensions relatively to the size of the bit, and a current will be caused to pass through said electrode, the return being effected either by the bit and drillpipes themselves, acting as a ground, or by another insulated electrode similarly incorporated into the body of the bit or carried thereby. Therefore this embodiment of the invention will comprise a special bit, fitted on its under surface with one or more insulated electrodes, which are connected by means of insulated conductors with a known or suitable electrical measurement instrument above ground, adapted to measure an electrical characteristic of the formation with which the under surface of the bit is in contact at the time.

Fig. 3 illustrates a combined drill and measurement system, comprising a drill bit having two insulated electrodes affixed to, or inserted into, its under surface; the drill hole being designated by numeral I, the bit by numeral 4, and the drill pipe, to which thebit is directly attached, by numeral 3, as in Fig. 1.

Two electrodes 5a, 5b, of relatively small dimensions, are countersunk in the under surface of bit 4, being embedded in blocks or casings 6 of insulating material, such as rubber or Bakelite. These electrodes are connected by insulated conductors-24 and 25, which pass through the bit, to other insulated conductors 26 and 21, respectively, inside the drill pipe 3. Conductors 26 and 21 are electrically connected at their ends to collector rings 28 and 29, respectively, said collector rings being carried by the grief stem, or being otherwise conveniently disposed. Brushes 30 and 3| are in contact with collector rings 28 and 29, respectively, which in 'turn are connected to the terminals 32 and 34, respectively, of a resistance measuring device, constituted for example by a Wheatstone bridge, as shown. In this case'each of the terminals 32, 34, constitutes one apex of the bridge, the other apices being designated 33 and 35 respectively. The bridge is fed by a source of current, 36, placed on diagonal 32-33, and a measuring instrument 31 (a galvanometer, for example) is placed on the diagonal 34-3 It is possible, by means of this assembly and in accordance with known methods, to measure the total resistance comprised between terminals 32 and 34, that is to say, the resistance of conductors 24, 25, 26 and 21, plus the resistance of the formation lying between the electrodes 5a, 51). As shown in the drawings (Fig. 3) the current passing through said-electrodes passes also through the still intact formation just beneath the bit; wherefore the resistance to the passage of current through the circuit is proportional to the true resistivity of the formation. Furthermore, owing to the relatively small size of electrodes 5a, 5b, this resistance is.considerable in comparison with the total resistances of the several conductors; and therefore the variations of the resistances of said conductors in function of their length and temperature, and that also of contacts 30, 3|, have no appreciable influence in practice on the precision of the measurements. Consequently, the resistance measured is, for practical purposes, proportional to that of the formation in contact with the underside of the bit. In order to determine the coeflicient of proportionality it is only necessary to measure above ground the resistance between electrodes 50. and b, seeing that the bit is placed in a medium of known resistivity.

The apparatus shown in Fig. 4 differs from that shown in Fig. 3 mainly in that, instead of two electrodes, placed as there shown, a single electrode 50, is used, which preferably is located in the axis of the bit, being insulated therefrom as described with reference to Fig. 3. Electrode 5c is connected (as described with reference to electrode 5a of Fig. 3) by an insulated conductor 28a to one of the terminals 34 of a resistivitymeasuring apparatus A above ground, such as shown in Fig. 3, the other terminal of which is connected at 39 to the drill pipe, acting as a ground, or directly to the ground if preferred.

The insulating material used for encasing the electrodes 5a, 5b and 50 should have as nearly as obtainable the same coefiicient of resistance to wear as the metal of the bit, so that the several parts of the bit will maintain the same relative positions.

Many modifications of the described arrangements can obviously be made within the scope of the invention as set forth in the appended claims.

What is claimed is:

1. Apparatus for continuously investigating drill holes during the drilling operation, comprising a drilling mechanism having a drill bit provided with an electrode which is aflixed thereto in such position as to be in contact with the drilling fluid while the drill is in operation, said electrode being connected by insulated means to one terminal of an electrical measuring instrument above ground, the other terminal thereof being suitably grounded.

2. Apparatus for continuously investigating drill holes during the drilling operation, comprising a drilling mechanism having a drill bit provided with an electrode in contact with the drill-- ing fluid, said electrode being fixed to the drill bit and forming a permanent part thereof but insulated therefrom, and insulated means connecting said electrode to one terminal of an electrical measuring instrument above ground, the other terminal of said instrument being grounded.

3. Apparatus for continuously investigating drill holes during'the drilling operation, comprising a drilling mechanism having a drill bit provided with an electrode amxed thereto but inthereby, and electrical measuring means includ-.

ing a circuit whereof said electrode forms one terminal and an electrical measuring instrument in said circuit.

5. Apparatus for investigating during the course of a drilling operation the formations contacted by the drill bit, which apparatus comprises: a drill hit, an insulated electrode on the under surface of said bit, and electrical measuring means including a circuit whereof said electrode forms one terminal and an electrical measuring instrument in said circuit.

6. Apparatus for investigating while a drilling operation is in progress the formations successively contacted by the drill bit, which apparatus comprises: a drill bit, a pair of insulated electrodes on the underside of said bit, an insulated electric circuit whereof each of said electrodes forms one terminal, and an electrical measuring device in said circuit.

7. A drilling bit having an electrode affixed thereto and forming a part thereof but electrically insulated therefrom.

8. A drilling bit having an electrode affixed to the underside thereof, said electrode forming a permanent part of the bit structure but being electrically insulated therefrom.

9. A drilling bit having a pair of electrodes affixed to the underside thereof, said electrodes forming permanent parts of the bit structure but being electrically insulated therefrom and adapted to constitute the respective terminals of an electrical circuit.

10. Apparatus for investigating drill holes during the drilling operation, comprising a drilling mechanism having a drill hit, an insulated electrode aflixed to the drill bit, and means for obtaining indications of spontaneous potentials existing between said electrode and a reference P int.

11. Apparatus for investigating earth formations encountered by a drill bit during the drilling of a bore hole, comprising a drill bit having an insulated electrode aflixed thereto and means for obtaining indications between said electrode and a ground point of an electrical characteristic of said formations in the vicinity of the electrode.

EUGENE G. LEONARDON. 

